I make two types of clear soup - one is beef and one is vegetable - and I use them as a base for all my other soups. As you probably don't have a piece of brisket laying around spare, I wont give you the beef recipe.
Here's my vegetable recipe - you can adapt it to use whatever veg you have available.
2 chopped carrots
quarter of a celeriac
1 chopped turnip
300g sliced leeks
2 halved, peeled onions
1.5 litres water
2 juniper berries
2 bay leaves
1 teaspoon mixed peppercorns
celery salt, sea salt & nutmeg to taste
a little oil
fresh parsley & tarragon (or 1 teaspoon of each if dried)
Saute all the veg in the oil until softened. Add all the other ingredients, bring to the boil and then cook over a low heat for one hour. Strain through a fine cloth. (If you don't have muslin, use a new J cloth).
It's easy to make and very nutritious.
I hope your operation is nothing serious and I wish you well with it. xx